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continuous rate 12.3 mb/s to 2.7 gb/s clock and data recovery ic with integrated limiting amp adn2812 rev. 0 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent ri ghts of analog devices. trademarks and registered trademarks are the prop erty of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 www.analog.com fax: 781.326.8703 ? 2004 analog devices, inc. all rights reserved. features serial data input: 12.3 mb/s to 2.7 gb/s exceeds sonet requirements for jitter transfer/ generation/tolerance quantizer sensitivity: 6 mv typical adjustable slice level: 100 mv patented clock recovery architecture loss of signal (los) detect range: 3 mv to 15 mv independent slice level adjust and los detector no reference clock required loss of lock indicator i 2 c? interface to access optional features single-supply operation: 3.3 v low power: 750 mw typical 5 mm 5 mm 32-lead lfcsp applications sonet oc-1/3/12/48 and all associated fec rates fibre channel, 2 fibre channel , gbe, hdtv, etc. wdm transponders regenerators/repeaters test equipment broadband cross-connects and routers product description the adn2812 provides the receiver functions of quantization, signal level detect, and clock and data recovery for continuous data rates from 12.3 mb/s to 2.7 gb/s. the adn2812 automati- cally locks to all data rates without the need for an external reference clock or programming. all sonet jitter requirements are met, including jitter transfer, jitter generation, and jitter tolerance. all specifications are quoted for ?40c to +85c ambient temperature, unless otherwise noted. this device, together with a pin diode and a tia preamplifier, can implement a highly integrated, low cost, low power fiber optic receiver. the receiver front end loss of signal (los) detector circuit indicates when the input signal level has fallen below a user- adjustable threshold. the los detect circuit has hysteresis to prevent chatter at the output. the adn2812 is available in a compact 5 mm 5 mm 32-lead chip scale package. functional block diagram 2 04228-0-001 s licep/n lol dataoutp/n los thradj clkoutp/n 2 vcc vee cf1 cf2 pin nin vref quantizer vco phase shifter phase detect frequency detect los detect data re-timing loop filter loop filter refclkp/n (optional) 2 figure 1.
adn2812 rev. 0 | page 2 of 28 table of contents specifications..................................................................................... 3 jitter specifications....................................................................... 4 output and timing specifications ............................................. 5 absolute maximum ratings............................................................ 6 thermal characteristics .............................................................. 6 esd caution.................................................................................. 6 timing characteristics..................................................................... 7 pin configuration and function descriptions............................. 8 typical performance characteristics ............................................. 9 i 2 c interface timing and internal register description ........... 10 terminology .................................................................................... 12 jitter specifications ......................................................................... 13 jitter generation ......................................................................... 13 jitter transfer............................................................................... 13 jitter tolerance ............................................................................ 13 theory of operation ...................................................................... 14 functional description.................................................................. 16 frequency acquisition............................................................... 16 limiting amplifier ..................................................................... 16 slice adjust .................................................................................. 16 loss of signal (los) detector .................................................. 16 lock detector operation .......................................................... 16 harmonic detector .................................................................... 17 squelch mode ............................................................................. 17 i2c interface ............................................................................... 18 reference clock (optional) ...................................................... 18 applications information .............................................................. 21 pcb design guidelines ............................................................. 21 dc-coupled application .......................................................... 23 coarse data rate readback look-up table............................... 24 outline dimensions ....................................................................... 26 ordering guide .......................................................................... 26 revision history revision 0: initial version
adn2812 rev. 0 | page 3 of 28 specifications t a = t min to t max , vcc = v min to v max , vee = 0 v, c f = 0.47 f, slicep = slicen = vee, input data pattern: prbs 2 23 ? 1, unless otherwise noted. table 1. parameter conditions min typ max unit quantizerdc characteristics input voltage range @ pin or nin, dc-coupled 1.8 2.8 v peak-to-peak differential input pin C nin 2.0 v input common mode level dc-coupled (see figure 28, figure 29, and figure 30) 2.3 2.5 2.8 v differential input sensitivity 2 23 ? 1 prbs, ac-coupled, 1 ber = 1 x 10 C10 10 6 mv p-p input overdrive (see figure 12) 5 3 mv p-p input offset 500 v input rms noise ber = 1 x 10 C10 290 v rms quantizerac characteristics data rate 12.3 2700 mb/s s11 @ 2.5 ghz ?15 db input resistance differential 100 ? input capacitance 0.65 pf quantizerslice adjustment gain slicep C slicen = 0.5 v 0.08 0.1 0.12 v/v differential control voltage input slicep C slicen C0.95 +0.95 v control voltage range dc level @ slicep or slicen vee 0.95 v slice threshold offset 1 mv loss of signal detect (los) loss of signal detect range (see figure 5) r thresh = 0 ? 12 15 17 mv r thresh = 100 k? 2.0 3.0 4.0 mv hysteresis (electrical) oc-48 r thresh = 0 ? 5.6 6 7.2 db r thresh = 100 k? 3.7 6 8.4 db oc-1 r thresh = 0 ? 5.6 6 7.2 db r thresh = 10 k? 2.0 4 6.7 db los assert time dc-coupled 2 500 ns los de-assert time dc-coupled 2 400 ns loss of lock detect (lol) vco frequency error for lol assert with respect to nominal 1000 ppm vco frequency error for lol de-assert with respect to nominal 250 ppm lol response time 12.3 mb/s 4 ms oc-12 1.0 s oc-48 1.0 s acquisition time lock to data mode oc-48 1.3 ms oc-12 2.0 ms oc-3 3.4 ms oc-1 9.8 ms 12.3 mb/s 40.0 ms optional lock to refclk mode 10.0 ms 1 pin and nin should be differentially driv en and ac-coupled for optimum sensitivity. 2 when ac-coupled, the los assert and de-assert time is dominated by the rc time constant of the ac coupling capacitor and the 5 0 ? input termination of the adn2812 input stage.
adn2812 rev. 0 | page 4 of 28 parameter conditions min typ max unit data rate readback accuracy coarse readback (see table 13) 10 % fine readback in addition to refclk accuracy data rate < 20 mb/s 200 ppm data rate > 20 mb/s 100 ppm power supply voltage 3.0 3.3 3.6 v power supply current 219 235 259 ma operating temperature range C40 +85 c jitter specifications t a = t min to t max , vcc = v min to v max , vee = 0 v, c f = 0.47 uf, slicep = slicen = vee, input data pattern: prbs 2 23 ? 1, unless otherwise noted. table 2. parameter conditions min typ max unit phase-locked loop characteristics jitter transfer bw oc-48 490 670 khz oc-12 71 108 khz oc-3 23 35 khz jitter peaking oc-48 0 0.03 db oc-12 0 0.03 db oc-3 0 0.03 db jitter generation oc-48, 12 khz to 20 mhz 0.001 0.002 ui rms 0.02 0.037 ui p-p oc-12, 12 khz to 5 mhz 0.001 0.002 ui rms 0.01 0.019 ui p-p oc-3, 12 khz to 1.3 mhz 0.001 0.002 ui rms 0.01 0.011 ui p-p jitter tolerance oc-48, 2 23 ? 1 prbs 600 hz 70 92 ui p-p 6 khz 19 45 ui p-p 100 khz 3.8 5 ui p-p 1 mhz 0.75 1 ui p-p 20 mhz 0.4 0.6 ui p-p oc-12, 2 23 ? 1 prbs 30 hz 3 100 ui p-p 300 hz 1 44 ui p-p 25 khz 2.5 ui p-p 250 khz 1 1.0 ui p-p oc-3, 2 23 ? 1 prbs 30 hz 1 50 ui p-p 300 hz 1 24 ui p-p 6500 hz 3.5 ui p-p 65 khz 1.0 ui p-p 3 jitter tolerance of the adn2812 at these jitter frequencies is better than what the test equipm ent is able to measure.
adn2812 rev. 0 | page 5 of 28 output and timing specifications table 3. parameter conditions min typ max unit cml ouput characteristics (clkoutp/n, dataoutp/n) single-ended output swing v se (see figure 3) 300 350 600 mv differential output swing v diff (see figure 3) 600 700 1200 mv output high voltage v oh vcc v output low voltage v ol vcc ? 0.6 vcc ? 0.35 vcc ? 0.3 v cml ouputs timing rise time 20% to 80% 95 112 ps fall time 80% to 20% 95 123 ps setup time t s (see figure 2), oc-48 150 200 250 ps hold time t h (see figure 2), oc-48 150 200 250 ps i 2 c interface dc characteristics lvcmos input high voltage v ih 0.7 vcc v input low voltage v il 0.3 vcc v input current v in = 0.1 vcc or v in = 0.9 vcc ?10.0 +10.0 a output low voltage v ol , i ol = 3.0 ma 0.4 v i 2 c interface timing (see figure 11) sck clock frequency 400 khz sck pulse width high t high 600 ns sck pulse width low t low 1300 ns start condition hold time t hd;sta 600 ns start condition setup time t su;sta 600 ns data setup time t su;dat 100 ns data hold time t hd;dat 300 ns sck/sda rise/fall time t r /t f 20 + 0.1 cb 4 300 ns stop condition setup time t su;sto 600 ns bus free time between a stop and a start t buf 1300 ns refclk characteristics optional lock to refclk mode input voltage range @ refclkp or refclkn v il 0 v v ih vcc v minimum differential input drive 100 mv p-p reference frequency 12.3 200 mhz required accuracy 100 ppm lvttl dc input characteristics input high voltage v ih 2.0 v input low voltage v il 0.8 v input high current i ih , v in = 2.4 v 5 a input low current i il , v in = 0.4 v ?5 a lvttl dc output characteristics output high voltage v oh , i oh = ?2.0 ma 2.4 v output low voltage v ol , i ol = 2.0 ma 0.4 v 4 c b = total capacitance of one bus line in pf. if mixed with hs-mode devices, faster fall-times are allowed (see table 6).
adn2812 rev. 0 | page 6 of 28 absolute maximum ratings t a = t min to t max , vcc = v min to v max , vee = 0 v, c f = 0.47 f, slicep = slicen = vee, unless otherwise noted. table 4. parameter rating supply voltage (vcc) 4.2 v minimum input voltage (all inputs) vee ? 0.4 v maximum input voltage (all inputs) vcc + 0.4 v maximum junction temperature 125c storage temperature ?65c to +150c lead temperature (soldering 10 s) 300c stress above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. thermal characteristics thermal resistance 32-lfcsp, 4-layer board with exposed paddle soldered to vee ja = 28c/w. esd caution esd (electrostatic discharge) sensitive device. electros tatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge wi thout detection. although this product features proprietary esd protection circuitry, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality.
adn2812 rev. 0 | page 7 of 28 timing characteristics 04228-0-002 clkoutp dataoutp/n t s t h figure 2. output timing 04228-0-004 outp outn outp?outn 0v v se v cml v se v diff figure 3. single-ended vs. differential output specifications
adn2812 rev. 0 | page 8 of 28 pin configuration and fu nction descriptions 04228-0-029 test1 1 vcc 2 vref 3 pin 1 indicator top view (not to scale) 24 vcc 23 vee 22 los 21 sda 32 test2 20 sck 19 saddr5 18 vcc 17 vee thradj 9 refclkp 10 refclkn 11 vcc 12 vee 13 cf2 14 cf1 15 lol 16 nin 4 pin 5 slicep 6 slicen 7 vee 8 31 vcc 30 vee 29 dataoutp 28 dataoutn 27 squelch 26 clkoutp 25 clkoutn adn2812* * there is an exposed pad on the bottom of the package that must be connected to gnd. figure 4. pin configuration table 5. pin function descriptions pin no. mnemonic type 1 description 1 test1 connect to vcc. 2 vcc p power for limamp, los. 3 vref ao internal vref voltage. decouple to gnd with a 0.1 f capacitor. 4 nin ai differential data input. cml. 5 pin ai differential data input. cml. 6 slicep ai differential slice level adjust input. 7 slicen ai differential slice level adjust input. 8 vee p gnd for limamp, los. 9 thradj ai los threshold setting resistor. 10 refclkp di differential refclk input. 12.3 mhz to 200 mhz. 11 refclkn di differential refclk input. 12.3 mhz to 200 mhz. 12 vcc p vco power. 13 vee p vco gnd. 14 cf2 ao frequency loop capacitor. 15 cf1 ao frequency loop capacitor. 16 lol do loss of lock indicator. lvttl active high. 17 vee p fll detector gnd. 18 vcc p fll detector power. 19 saddr5 di slave address bit 5. 20 sck di i 2 c clock input. 21 sda di i 2 c data input. 22 los do loss of signal detect output. active high. lvttl. 23 vee p output buffer, i 2 c gnd. 24 vcc p output buffer, i 2 c power. 25 clkoutn do differential re covered clock output. cml. 26 clkoutp do differential re covered clock output. cml. 27 squelch di disable clock and data outputs. active high. lvtll. 28 dataoutn do differential recovered data output. cml. 29 dataoutp do differential recovered data output. cml. 30 vee p phase detector, phase shifter gnd. 31 vcc p phase detector, phase shifter power. 32 test2 connect to vcc. exposed pad pad p connect to gnd 1 type: p = power, ai = analog input, ao = analog output, di = digital input, do = digital output.
adn2812 rev. 0 | page 9 of 28 typical performance characteristics 04228-0-003 16 14 12 1 10 100 r th ( ? ) 1k 10k 100k 10 8 6 4 2 trip point (mv p-p) figure 5. los comparator trip point programming 04228-0-030 1000 1 10 100 1k 10k 100k 1m 10m jitter frequency (hz) 100m 0.1 1 10 100 jitter amplitude (ui) adn2812 tolerance sonet requirement mask sonet objective mask equipment limit figure 6. typical measured jitter tolerance oc-48
adn2812 rev. 0 | page 10 of 28 i 2 c interface timing and internal register description 04228-0-005 1a500000x msb = 1 set by pin 19 0 = wr 1 = rd slave address [6...0] r/w ctrl. figure 7. slave address configuration 04228-0-006 s slave addr, lsb = 0 (wr) a(s) a(s) a(s) data sub addr a(s) p data figure 8. i 2 c write data transfer 04228-0-007 s s = start bit p = stop bit a(s) = acknowledge by slave a(m) = acknowledge by master a(m) = lack of acknowledge by master s slave addr, lsb = 0 (wr) slave addr, lsb = 1 (rd) a(s) a(s) sub addr a(s) data a(m) data p a(m) figure 9. i 2 c read data transfer 04228-0-008 start bit s stop bit p ack ack wr ack d0 d7 a0 a7 a5 a6 sladdr[4...0] slave address sub address data sub addr[6...1] data[6...1] sck sda figure 10. i 2 c data transfer timing 04228-0-009 t buf sda ssps sck t f t low t r t f t hd;sta t hd;dat t su;dat t high t su;sta t su;sto t hd;sta t r figure 11. i 2 c port timing diagram
adn2812 rev. 0 | page 11 of 28 table 6. internal register map 1 reg name r/w address d7 d6 d5 d4 d3 d2 d1 d0 freq0 r 0x0 msb lsb freq1 r 0x1 msb lsb freq2 r 0x2 0 msb lsb rate r 0x3 coarse_rd[8] msb coarse datarate readback coarse_rd[1] misc r 0x4 x x los status static lol lol status datarate measure complete x coarse_ rd[0] lsb ctrla w 0x8 f ref range datarate/div_f ref ratio measure datarate lock to reference ctrlb w 0x9 config lol reset misc[4] system reset 0 reset misc[2] 0 0 0 ctrlc w 0x11 0 0 0 0 0 config los squelch mode 0 1 all writeable registers default to 0x00. table 7. miscellaneous register, misc los status static lol lol status datarate measurement complete coarse rate readback lsb d7 d6 d5 d4 d3 d2 d1 d0 x x 0 = no loss of signal 0 = waiting for next lol 0 = locked 0 = measuring datarate x coarse_rd[0] 1 = loss of signal 1 = static lol until reset 1 = acquiring 1 = measurement complete table 8. control register, ctrla 1 f ref range datarate/div_f ref ratio measure datarate lock to reference d7 d6 d5 d4 d3 d2 d1 d0 0 0 12.3 mhz to 25 mhz 0 0 0 0 1 set to 1 to measure datarate 0 = lock to input data 0 1 25 mhz to 50 mhz 0 0 0 1 2 1 = lock to reference clock 1 0 50 mhz to 100 mhz 0 0 1 0 4 1 1 100 mhz to 200 mhz n 2 n 1 0 0 0 256 1 where div_f ref is the divided down reference referred to the 12.3 mhz to 25 mhz band (see the reference clock (optional) section). table 9. control register, ctrlb config lol reset misc[4] system reset reset misc[2] d7 d6 d5 d4 d3 d2 d1 d0 0 = lol pin normal operation 1 = lol pin is static lol write a 1 followed by 0 to reset misc[4] write a 1 followed by 0 to reset adn2812 set to 0 write a 1 followed by 0 to reset misc[2] set to 0 set to 0 set to 0 table 10. control register, ctrlc config los squelch mode d7 d6 d5 d4 d3 d2 d1 d0 0 = active high los 0 = squelch clk and data set to 0 set to 0 set to 0 set to 0 set to 0 set to 0 1 = active low los 1 = squelch clk or data
adn2812 rev. 0 | page 12 of 28 terminology input sensitivity and input overdrive sensitivity and overdrive specifications for the quantizer involve offset voltage, gain, and noise. the relationship between the logic output of the quantizer and the analog voltage input is shown in figure 12. for sufficiently large positive input voltage, the output is always logic 1 and, similarly for negative inputs, the output is always logic 0. however, the transitions between output logic levels 1 and 0 are not at precisely defined input voltage levels, but occur over a range of input voltages. within this range of input voltages, the output might be either 1 or 0, or it might even fail to attain a valid logic state. the width of this zone is determined by the input voltage noise of the quantizer. the center of the zone is the quantizer input offset voltage. input overdrive is the magnitude of signal required to guarantee the correct logic level with 1 10 ?10 confidence level. 04228-0-010 noise output input (v p-p) offset overdrive sensitivity (2 overdrive) 1 0 figure 12. input sensitivity and input overdrive single-ended vs. differential ac coupling is typically used to drive the inputs to the quantizer. the inputs are internally dc biased to a common- mode potential of ~2.5 v. driving the adn2812 single-ended and observing the quantizer input with an oscilloscope probe at the point indicated in figure 13 shows a binary signal with an average value equal to the common-mode potential and instantaneous values both above and below the average value. it is convenient to measure the peak-to-peak amplitude of this signal and call the minimum required value the quantizer sensitivity. referring to figure 13, because both positive and negative offsets need to be accommodated, the sensitivity is twice the overdrive. the adn2812 quantizer typically has 6 mv p-p sensitivity. 04228-0-011 scope probe pin 50 ? 3k ? 2.5v 50 ? vref adn2812 quantizer + ? 10mv p-p vref figure 13. single-ended sensitivity measurement driving the adn2812 differentially (see figure 14), sensitivity seems to improve from observing the quantizer input with an oscilloscope probe. this is an illusion caused by the use of a single-ended probe. a 5 mv p-p signal appears to drive the adn2812 quantizer. however, the single-ended probe measures only half the signal. the true quantizer input signal is twice this value, because the other quantizer input is a complementary signal to the signal being observed. 04228-0-012 scope probe pin 50 ? 3k ? 2.5v 50 ? vref quantizer + ? nin 5mv p-p vref 5mv p-p vref figure 14. differential sensitivity measurement los response time los response time is the delay between removal of the input signal and indication of loss of signal (los) at the los output, pin 22. when the inputs are dc-coupled, the los assert time of the ad2812 is 500 ns typically and the de-assert time is 400 ns typically,. in practice, the time constant produced by the ac coupling at the quantizer input and the 50 ? on-chip input termination determines the los response time.
adn2812 rev. 0 | page 13 of 28 jitter specifications the adn2812 cdr is designed to achieve the best bit-error- rate (ber) performance and exceeds the jitter transfer, genera- tion, and tolerance specifications proposed for sonet/sdh equipment defined in the telcordia technologies specification. jitter is the dynamic displacement of digital signal edges from their long-term average positions, measured in unit intervals (ui), where 1 ui = 1 bit period. jitter on the input data can cause dynamic phase errors on the recovered clock sampling edge. jitter on the recovered clock causes jitter on the retimed data. the following sections briefly summarize the specifications of jitter generation, transfer, and tolerance in accordance with the telcordia document (gr-253-core, issue 3, september 2000) for the optical interface at the equipment level and the adn2812 performance with respect to those specifications. jitter generation the jitter generation specification limits the amount of jitter that can be generated by the device with no jitter and wander applied at the input. for oc-48 devices, the band-pass filter has a 12 khz high-pass cutoff frequency with a roll-off of 20 db/decade, and a low-pass cutoff frequency of at least 20 mhz. the jitter generated must be less than 0.01 ui rms, and must be less than 0.1 ui p-p. jitter transfer the jitter transfer function is the ratio of the jitter on the output signal to the jitter applied on the input signal versus the frequency. this parameter measures the limited amount of the jitter on an input signal that can be transferred to the output signal (see figure 15). 04228-0-013 0.1 acceptable range f c jitter frequency (khz) slope = ?20db/decade jitter gain (db) figure 15. jitter transfer curve jitter tolerance the jitter tolerance is defined as the peak-to-peak amplitude of the sinusoidal jitter applied on the input signal, which causes a 1 db power penalty. this is a stress test intended to ensure that no additional penalty is incurred under the operating conditions (see figure 16). 04228-0-014 15.00 1.50 0.15 f 0 f 1 f 2 f 3 f 4 jitter frequency (khz) slope = ?20db/decade input jitter amplitude (ui p-p) figure 16. sonet jitter tolerance mask
adn2812 rev. 0 | page 14 of 28 theory of operation the adn2812 is a delay- and phase-locked loop circuit for clock recovery and data retiming from an nrz encoded data stream. the phase of the input data signal is tracked by two separate feedback loops, which share a common control voltage. a high speed delay-locked loop path uses a voltage controlled phase shifter to track the high frequency components of input jitter. a separate phase control loop, comprised of the vco, tracks the low frequency components of input jitter. the initial frequency of the vco is set by yet a third loop, which compares the vco frequency with the input data frequency and sets the coarse tuning voltage. the jitter tracking phase-locked loop controls the vco by the fine-tuning control. the delay- and phase-loops together track the phase of the input data signal. for example, when the clock lags input data, the phase detector drives the vco to higher frequency, and also increases the delay through the phase shifter; both these actions serve to reduce the phase error between the clock and data. the faster clock picks up phase, while the delayed data loses phase. because the loop filter is an integrator, the static phase error is driven to zero. another view of the circuit is that the phase shifter implements the zero required for frequency compensation of a second- order phase-locked loop, and this zero is placed in the feedback path and, thus, does not appear in the closed-loop transfer function. jitter peaking in a conventional second-order phase- locked loop is caused by the presence of this zero in the closed- loop transfer function. because this circuit has no zero in the closed-loop transfer, jitter peaking is minimized. the delay- and phase-loops together simultaneously provide wide-band jitter accommodation and narrow-band jitter filtering. the linearized block diagram in figure 17 shows that the jitter transfer function, z(s)/x(s), is a second-order low-pass providing excellent filtering. note that the jitter transfer has no zero, unlike an ordinary second-order phase-locked loop. this means that the main pll loop has virtually zero jitter peaking (see figure 18). this makes this circuit ideal for signal regen- erator applications, where jitter peaking in a cascade of regenerators can contribute to hazardous jitter accumulation. the error transfer, e(s)/x(s), has the same high-pass form as an ordinary phase-locked loop. this transfer function is free to be optimized to give excellent wide-band jitter accommodation, because the jitter transfer function, z(s)/x(s), provides the narrow-band jitter filtering. 04228-0-015 x(s) z(s) recovered clock e(s) input data d/sc psh o/s 1/n d = phase detector gain o = vco gain c = loop integrator psh = phase shifter gain n = divide ratio = 1 cn do s 2 + n psh o s+ 1 z(s) x(s) jitter transfer function = s 2 s 2 d psh c s ++ do cn e(s) x(s) tracking error transfer function figure 17. adn2812 pll/dll architecture adn2812 z(s) x(s) 04228-0-016 frequency (khz) jitter peaking in ordinary pll jitter gain (db) o n psh d psh c figure 18. adn2812 jitter response vs. conventional pll the delay- and phase-loops contribute to overall jitter accom- modation. at low frequencies of input jitter on the data signal, the integrator in the loop filter provides high gain to track large jitter amplitudes with small phase error. in this case, the vco is frequency modulated and jitter is tracked as in an ordinary phase-locked loop. the amount of low frequency jitter that can be tracked is a function of the vco tuning range. a wider tuning range gives larger accommodation of low frequency jitter. the internal loop control voltage remains small for small phase errors, so the phase shifter remains close to the center of its range and thus contributes little to the low frequency jitter accommodation.
adn2812 rev. 0 | page 15 of 28 at medium jitter frequencies, the gain and tuning range of the vco are not large enough to track input jitter. in this case, the vco control voltage becomes large and saturates, and the vco frequency dwells at one extreme of its tuning range or the other. the size of the vco tuning range, therefore, has only a small effect on the jitter accommodation. the delay-locked loop control voltage is now larger, and so the phase shifter takes on the burden of tracking the input jitter. the phase shifter range, in ui, can be seen as a broad plateau on the jitter tolerance curve. the phase shifter has a minimum range of 2 ui at all data rates. the gain of the loop integrator is small for high jitter frequencies, so that larger phase differences are needed to make the loop control voltage big enough to tune the range of the phase shifter. large phase errors at high jitter frequencies cannot be tolerated. in this region, the gain of the integrator determines the jitter accommodation. because the gain of the loop integrator declines linearly with frequency, jitter accom- modation is lower with higher jitter frequency. at the highest frequencies, the loop gain is very small, and little tuning of the phase shifter can be expected. in this case, jitter accommodation is determined by the eye opening of the input data, the static phase error, and the residual loop jitter generation. the jitter accommodation is roughly 0.5 ui in this region. the corner frequency between the declining slope and the flat region is the closed loop bandwidth of the delay-locked loop, which is roughly 3 mhz at oc-48.
adn2812 rev. 0 | page 16 of 28 functional description frequency acquisition the adn2812 acquires frequency from the data over a range of data frequencies from 12.3 mb/s to 2.7 gb/s. the lock detector circuit compares the frequency of the vco and the frequency of the incoming data. when these frequencies differ by more than 1000 ppm, lol is asserted. this initiates a frequency acquisition cycle. the vco frequency is reset to the bottom of its range, which is 12.3 mhz. the frequency detector then compares this vco frequency and the incoming data frequency and increments the vco frequency, if necessary. initially, the vco frequency is incremented in large steps to aid fast acquisi- tion. as the vco frequency approaches the data frequency, the step size is reduced until the vco frequency is within 250 ppm of the data frequency, at which point lol is de-asserted. once lol is de-asserted, the frequency-locked loop is turned off. the pll/dll pulls in the vco frequency the rest of the way until the vco frequency equals the data frequency. the frequency loop requires a single external capacitor between cf1 and cf2, pins 14 and 15. a 0.47 f 20%, x7r ceramic chip capacitor with < 10 na leakage current is recommended. leakage current of the capacitor can be calculated by dividing the maximum voltage across the 0.47 f capacitor, ~3 v, by the insulation resistance of the capacitor. the insulation resistance of the 0.47 uf capacitor should be greater than 300 m?. limiting amplifier the limiting amplifier has differential inputs (pin/nin), which are internally terminated with 50 ? to an on-chip voltage reference (vref = 2.5 v typically). the inputs are typically ac-coupled externally, although dc coupling is possible as long as the input common mode voltage remains above 2.5 v (see figure 28, figure 29, and figure 30 in the applications information section). input offset is factory trimmed to achieve better than 6 mv typical sensitivity with minimal drift. the limiting amplifier can be driven differentially or single-ended. slice adjust the quantizer slicing level can be offset by 100 mv to mitigate the effect of amplified spontaneous emission (ase) noise or duty cycle distortion by applying a differential voltage input of up to 0.95 v to slicep/n inputs. if no adjustment of the slice level is needed, slicep/n should be tied to vee. the gain of the slice adjustment is ~0.1 v/v. loss of signal (los) detector the receiver front end los detector circuit detects when the input signal level has fallen below a user-adjustable threshold. the threshold is set with a single external resistor from pin 9, thradj, to vee. the los comparator trip point-versus- resistor value is illustrated in figure 5. if the input level to the adn2812 drops below the programmed los threshold, the output of the los detector, los pin 22, is asserted to a logic 1. the los detectors response time is ~500 ns by design, but is dominated by the rc time constant in ac-coupled applications. the los pin defaults to active high. however, by setting bit ctrlc[2] to 1, the los pin is configured as active low. there is typically 6 db of electrical hysteresis designed into the los detector to prevent chatter on the los pin. this means that, if the input level drops below the programmed los threshold causing the los pin to assert, the los pin is not de- asserted until the input level has increased to 6 db (2) above the los threshold (see figure 19). 04228-0-017 hysteresis los output input level los threshold t input voltage (v diff ) figure 19. los detector hysteresis the los detector and the slice level adjust can be used simultaneously on the adn2812. this means that any offset added to the input signal by the slice adjust pins does not affect the los detectors measurement of the absolute input level. lock detector operation the lock detector on the adn2812 has three modes of operation: normal mode, refclk mode, and static lol mode. normal mode in normal mode, the adn2812 is a continuous rate cdr that locks onto any data rate from 12.3 mb/s to 2.7 gb/s without the use of a reference clock as an acquisition aid. in this mode, the lock detector monitors the frequency difference between the vco and the input data frequency, and de-asserts the loss of lock signal, which appears on lol pin 16, when the vco is within 250 ppm of the data frequency. this enables the d/pll, which pulls the vco frequency in the remaining amount and also acquires phase lock. once locked, if the input frequency error exceeds 1000 ppm (0.1%), the loss of lock signal is re- asserted and control returns to the frequency loop, which begins a new frequency acquisition starting at the lowest point in the vco operating range, 12.3 mhz. the lol pin remains asserted until the vco locks onto a valid input data stream to
adn2812 rev. 0 | page 17 of 28 within 250 ppm frequency error. this hysteresis is shown in figure 20. 04228-0-018 lol 0 ?250 250 1000 f vco error (ppm) ?1000 1 figure 20. transfer function of lol lol detector operation us ing a reference clock in this mode, a reference clock is used as an acquisition aid to lock the adn2812 vco. lock to reference mode is enabled by setting ctrla[0] to 1. the user also needs to write to the ctrla[7:6] and ctrla[5:2] bits in order to set the reference frequency range and the divide ratio of the data rate with respect to the reference frequency. for more details, see the reference clock (optional) section. in this mode, the lock detector monitors the difference in frequency between the divided down vco and the divided down reference clock. the loss of lock signal, which appears on the lol pin 16, is de- asserted when the vco is within 250 ppm of the desired frequency. this enables the d/pll, which pulls the vco frequency in the remaining amount with respect to the input data and also acquires phase lock. once locked, if the input frequency error exceeds 1000 ppm (0.1%), the loss of lock signal is re-asserted and control returns to the frequency loop, which re-acquires with respect to the reference clock. the lol pin remains asserted until the vco frequency is within 250 ppm of the desired frequency. this hysteresis is shown in figure 20. static lol mode the adn2812 implements a static lol feature, which indicates if a loss of lock condition has ever occurred and remains asserted, even if the adn2812 regains lock, until the static lol bit is manually reset. the i 2 c register bit, misc[4], is the static lol bit. if there is ever an occurrence of a loss of lock condition, this bit is internally asserted to logic high. the misc[4] bit remains high even after the adn2812 has re- acquired lock to a new data rate. this bit can be reset by writing a 1 followed by 0 to i 2 c register bit ctrlb[6]. once reset, the misc[4] bit remains de-asserted until another loss of lock condition occurs. wr iting a 1 to i 2 c register bit ctrlb[7] causes the lol pin, pin 16, to become a static lol indicator. in this mode, the lol pin mirrors the contents of the misc[4] bit and has the functionality described in the previous paragraph. the ctrlb[7] bit defaults to 0. in this mode, the lol pin operates in the normal operating mode, that is, it is asserted only when the adn2812 is in acquisition mode and de-asserts when the adn2812 has re-acquired lock. harmonic detector the adn2812 provides a harmonic detector, which detects whether or not the input data has changed to a lower harmonic of the data rate that the vco is currently locked onto. for example, if the input data instantaneously changes from oc-48, 2.488 gb/s, to an oc-12, 622.080 mb/s bit stream, this could be perceived as a valid oc-48 bit stream, because the oc-12 data pattern is exactly 4 slower than the oc-48 pattern. so, if the change in data rate is instantaneous, a 101 pattern at oc-12 would be perceived by the adn2812 as a 111100001111 pattern at oc-48. if the change to a lower harmonic is instantaneous, a typical cdr could remain locked at the higher data rate. the adn2812 implements a harmonic detector that automati- cally identifies whether or not the input data has switched to a lower harmonic of the data rate that the vco is currently locked onto. when a harmonic is identified, the lol pin is asserted and a new frequency acquisition is initiated. the adn2812 automatically locks onto the new data rate, and the lol pin is de-asserted. however, the harmonic detector does not detect higher harmonics of the data rate. if the input data rate switches to a higher harmonic of the data rate the vco is currently locked onto, the vco loses lock, the lol pin is asserted, and a new frequency acquisition is initiated. the adn2812 automatically locks onto the new data rate. the time to detect lock to harmonic is 16,384 ( t d /) where: 1/ t d is the new data rate. for example, if the data rate is switched from oc-48 to oc-12, then t d = 1/622 mhz. is the data transition density. most coding schemes seek to ensure that = 0.5, for example, prbs, 8b/10b. when the adn2812 is placed in lock to reference mode, the harmonic detector is disabled. squelch mode two squelch modes are available with the adn2812. squelch dataout and clkout mode is selected when ctrlc[1] = 0 (default mode). in this mode, when the squelch input, pin 27, is driven to a ttl high state, both the clock and data outputs are set to the zero state to suppress downstream processing. if the squelch function is not required, pin 27 should be tied to vee. squelch dataout or clkout mode is selected when ctrlc[1] is 1. in this mode, when the squelch input is driven to a high state, the dataout pins are squelched. when the squelch input is driven to a low state, the clkout pins are squelched. this is especially useful in repeater applications, where the recovered clock may not be needed.
adn2812 rev. 0 | page 18 of 28 i 2 c interface the adn2812 supports a 2-wire, i 2 c compatible, serial bus driving multiple peripherals. two inputs, serial data (sda) and serial clock (sck), carry information between any devices connected to the bus. each slave device is recognized by a unique address. the adn2812 has two possible 7-bit slave addresses for both read and write operations. the msb of the 7-bit slave address is factory programmed to 1. b5 of the slave address is set by pin 19, saddr5. slave address bits [4:0] are defaulted to all 0s. the slave address consists of the 7 msbs of an 8-bit word. the lsb of the word sets either a read or write operation (see figure 7). logic 1 corresponds to a read operation, while logic 0 corresponds to a write operation. to control the device on the bus, the following protocol must be followed. first, the master initiates a data transfer by establish- ing a start condition, defined by a high to low transition on sda while sck remains high. this indicates that an address/data stream follows. all peripherals respond to the start condition and shift the next eight bits (the 7-bit address and the r/w bit). the bits are transferred from msb to lsb. the peripheral that recognizes the transmitted address responds by pulling the data line low during the ninth clock pulse. this is known as an acknowledge bit. all other devices withdraw from the bus at this point and maintain an idle condition. the idle condition is where the device monitors the sda and sck lines waiting for the start condition and correct transmitted address. the r/w bit determines the direction of the data. logic 0 on the lsb of the first byte means that the master writes information to the peripheral. logic 1 on the lsb of the first byte means that the master reads information from the peripheral. the adn2812 acts as a standard slave device on the bus. the data on the sda pin is 8 bits long supporting the 7-bit addresses plus the r/w bit. the adn2812 has 8 subaddresses to enable the user-accessible internal registers (see table 1 through table 7). it, therefore, interprets the first byte as the device address and the second byte as the starting subaddress. autoincrement mode is supported, allowing data to be read from or written to the starting subaddress and each subsequent address without manually addressing the subsequent subaddress. a data transfer is always terminated by a stop condition. the user can also access any unique subaddress register on a one-by-one basis without updating all registers. stop and start conditions can be detected at any stage of the data transfer. if these conditions are asserted out of sequence with normal read and write operations, then they cause an immediate jump to the idle condition. during a given sck high period, the user should issue one start condition, one stop condition, or a single stop condition followed by a single start condition. if an invalid subaddress is issued by the user, the adn2812 does not issue an acknowledge and returns to the idle condition. if the user exceeds the highest subaddress while reading back in autoincrement mode, then the highest subad- dress register contents continue to be output until the master device issues a no-acknowledge. this indicates the end of a read. in a no-acknowledge condition, the sdata line is not pulled low on the ninth pulse. see figure 8 and figure 9 for sample read and write data transfers and figure 10 for a more detailed timing diagram. reference clock (optional) a reference clock is not required to perform clock and data recovery with the adn2812. however, support for an optional reference clock is provided. the reference clock can be driven differentially or single-ended. if the reference clock is not being used, then refclkp should be tied to vcc, and refclkn can be left floating or tied to vee (the inputs are internally terminated to vcc/2). see figure 21 through figure 23 for sample configurations. the refclk input buffer accepts any differential signal with a peak-to-peak differential amplit ude of greater than 100 mv (for example, lvpecl or lvds) or a standard single-ended low voltage ttl input, providing maximum system flexibility. phase noise and duty cycle of the reference clock are not critical and 100 ppm accuracy is sufficient. 04228-0-019 100k ? vcc/2 100k ? adn2812 refclkp 10 11 refclkn buffer figure 21. differential refclk configuration 04228-0-020 100k ? vcc/2 100k ? adn2812 refclkp out refclkn buffer vcc clk osc figure 22. single-ended refclk configuration 04228-0-021 100k ? vcc/2 100k ? adn2812 refclkp 10 11 nc refclkn buffer vcc figure 23. no refclk configuration
adn2812 rev. 0 | page 19 of 28 the two uses of the reference clock are mutually exclusive. the reference clock can be used either as an acquisition aid for the adn2812 to lock onto data, or to measure the frequency of the incoming data to within 0.01%. (there is the capability to measure the data rate to approximately 10 % without the use of a reference clock.) the modes are mutually exclusive, because, in the first use, the user knows exactly what the data rate is and wants to force the part to lock onto only that data rate; in the second use, the user does not know what the data rate is and wants to measure it. lock to reference mode is enabled by writing a 1 to i 2 c register bit ctrla[0]. fine data rate readback mode is enabled by writing a 1 to i 2 c register bit ctrla[1]. writing a 1 to both of these bits at the same time causes an indeterminate state and is not supported. using the reference clock to lock onto data in this mode, the adn2812 locks onto a frequency derived from the reference clock according to the following equation: data rate /2 ctrla[5:2] = refclk /2 ctrla[7:6] the user must know exactly what the data rate is, and provide a reference clock that is a function of this rate. the adn2812 can still be used as a continuous rate device in this configuration, provided that the user has the ability to provide a reference clock that has a variable frequency (see application note an-632). the reference clock can be anywhere between 12.3 mhz and 200 mhz. by default, the adn2812 expects a reference clock of between 12.3 mhz and 25 mhz. if it is between 25 mhz and 50 mhz, 50 mhz and 100 mhz, or 100 mhz and 200 mhz, the user needs to configure the adn2812 to use the correct reference frequency range by setting two bits of the ctrla register, ctrla[7:6]. table 11. ctrla settings ctrla[7:6] range (mhz) ctrla[5:2] ratio 00 12.3 to 25 0000 1 01 25 to 50 0001 2 10 50 to 100 n 2 n 11 100 to 200 1000 256 the user can specify a fixed integer multiple of the reference clock to lock onto using ctrla[5:2], where ctrla should be set to the data rate/div_f ref , where div_f ref represents the divided-down reference referred to the 12.3 mhz to 25 mhz band. for example, if the reference clock frequency was 38.88 mhz and the input data rate was 622.08 mb/s, then ctrla[7:6] would be set to [01] to give a divided-down reference clock of 19.44 mhz. ctrla[5:2] would be set to [0101], that is, 5, because 622.08 mb/s/19.44 mhz = 2 5 in this mode, if the adn2812 loses lock for any reason, it relocks onto the reference clock and continues to output a stable clock. while the adn2812 is operating in lock to reference mode, if the user ever changes the reference frequency, the f ref range (ctrla[7:6]), or the f ref ratio (ctrla[5:2]), this must be followed by writing a 0 to 1 transition into the ctrla[0] bit to initiate a new lock to reference command. using the reference clock to measure data frequency the user can also provide a reference clock to measure the recovered data frequency. in this case, the user provides a reference clock, and the adn2812 compares the frequency of the incoming data to the incoming reference clock and returns a ratio of the two frequencies to 0.01% (100 ppm). the accuracy error of the reference clock is added to the accuracy of the adn2812 data rate measurement. for example, if a 100-ppm accuracy reference clock is used, the total accuracy of the measurement is within 200 ppm. the reference clock can range from 12.3 mhz and 200 mhz. the adn2812 expects a reference clock between 12.3 mhz and 25 mhz by default. if it is between 25 mhz and 50 mhz, 50 mhz and 100 mhz, or 100 mhz and 200 mhz, the user needs to configure the adn2812 to use the correct reference frequency range by setting two bits of the ctrla register, ctrla[7:6]. using the reference clock to determine the frequency of the incoming data does not affect the manner in which the part locks onto data. in this mode, the reference clock is used only to determine the frequency of the data. for this reason, the user does not need to know the data rate to use the reference clock in this manner. prior to reading back the data rate using the reference clock, the ctrla[7:6] bits must be set to the appropriate frequency range with respect to the reference clock being used. a fine data rate readback is then executed as follows: step 1: write a 1 to ctrla[1]. this enables the fine data rate measurement capability of the adn2812. this bit is level sensitive and does not need to be reset to perform subsequent frequency measurements. step 2: reset misc[2] by writing a 1 followed by a 0 to ctrlb[3]. this initiates a new data rate measurement. step 3: read back misc[2]. if it is 0, then the measurement is not complete. if it is 1, then the measurement is complete and the data rate can be read back on freq[22:0]. the time for a data rate measurement is typically 80 ms. step 4: read back the data ra te from registers freq2[6:0], freq1[7:0], and freq0[7:0].
adn2812 rev. 0 | page 20 of 28 use the following equation to determine the data rate: [] () ) _ 14 ( 2 / 0 .. 22 rate sel refclk datarate f freq f + = where: freq[22:0] is the reading from freq2[6:0] (msbyte), freq1[7:0], and freq0[7:0] (lsbyte). table 12. d22 d21...d17 d16 d15 d14...d9 d8 d7 d6...d1 d0 freq2[6:0] freq1[7:0] freq0[7:0] f datarate is the data rate (mb/s). f refclk is the refclk frequency (mhz). sel_rate is the setting from ctrla[7:6]. for example, if the reference clock frequency is 32 mhz, sel_rate = 1, since the ctrla[7:6] setting would be [01], because the reference frequency would fall into the 25 mhz to 50 mhz range. assume for this example that the input data rate is 2.488 gb/s (oc-48). after following steps 1 through 4, the value that is read back on freq[22:0] = 0x26e010, which is equal to 2.5477 10 6 . plugging this value into the equation yields () ( ) gb/s 488 . 2 2 / 6 e 32 6 e 5477 . 2 ) 1 14 ( = + if subsequent frequency measurements are required, ctrla[1] should remain set to 1. it does not need to be reset. the measurement process is reset by writing a 1 followed by a 0 to ctrlb[3]. this initiates a new data rate measurement. follow steps 2 through 4 to read back the new data rate. note: a data rate readback is valid only if lol is low. if lol is high, the data rate readback is invalid. additional features available via the i 2 c interface coarse data rate readback the data rate can be read back over the i 2 c interface to approximately + 10% without the need of an external reference clock. a 9-bit register, coarse_rd[8:0], can be read back when lol is de-asserted. the 8 msbs of this register are the contents of the rate[7:0] register. the lsb of the coarse_rd register is bit misc[0]. table 13 provides coarse data rate readback to within 10%. los configuration the los detector output, los pin 22, can be configured to be either active high or active low. if ctrlc[2] is set to logic 0 (default), the los pin is active high when a loss of signal condition is detected. writing a 1 to ctrlc[2] configures the los pin to be active low when a loss of signal condition is detected. system reset a frequency acquisition can be initiated by writing a 1 followed by a 0 to the i 2 c register bit ctrlb[5]. this initiates a new frequency acquisition while keeping the adn2812 in the operating mode that it was previously programmed to in registers ctrl[a], ctrl[b], and ctrl[c].
adn2812 rev. 0 | page 21 of 28 applications information pcb design guidelines proper rf pcb design techniques must be used for optimal performance. power supply connections and ground planes use of one low impedance ground plane is recommended. the vee pins should be soldered directly to the ground plane to reduce series inductance. if the ground plane is an internal plane and connections to the ground plane are made through vias, multiple vias can be used in parallel to reduce the series inductance, especially on pin 23, which is the ground return for the output buffers. the exposed pad should be connected to the gnd plane using plugged vias so that solder does not leak through the vias during reflow. use of a 10 f electrolytic capacitor between vcc and vee is recommended at the location where the 3.3 v supply enters the pcb. when using 0.1 f and 1 nf ceramic chip capacitors, they should be placed between the ic power supply vcc and vee, as close as possible to the adn2812 vcc pins. if connections to the supply and ground are made through vias, the use of multiple vias in parallel helps to reduce series inductance, especially on pin 24, which supplies power to the high speed clkoutp/clkoutn and dataoutp/ dataoutn output buffers. refer to the schematic in figure 24 for recommended connections. by using adjacent power supply and gnd planes, excellent high frequency decoupling can be realized by using close spacing between the planes. this capacitance is given by ( ) pf 88 . 0 a/d c r plane = where: r is the dielectric constant of the pcb material. a is the area of the overlap of power and gnd planes (cm 2 ). d is the separation between planes (mm). for fr-4, r = 4.4 mm and 0.25 mm spacing, c ~15 pf/cm 2 . 04228-0-022 r th nc nc = no connect 1 2 3 4 5 6 7 8 test1 vcc vref nin pin slicep slicen vee vcc 50 ? transmission lines 100 ? 4 vcc vee los sda sck saddr5 vcc vee test2 vcc vee dataoutp dataoutn squelch clkoutp clkoutn thradj refclkp refclkn vcc vee cf2 cf1 lol 9 10111213141516 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 exposed pad tied off to vee plane with vias clkoutn clkoutp dataoutn dataoutp vcc tia 50 ? 50 ? c in c in 1nf 0.1 f 0.1 f 10 f + 0.1 f 1nf vcc vcc vcc c c i 2 c controller 0.1 f 1nf 0.1 f vcc 1nf 0.1 f 0.47 f 20% >300m ? insulation resistance 1nf figure 24. typical adn2812 applications circuit
adn2812 rev. 0 | page 22 of 28 transmission lines use of 50 ? transmission lines is required for all high frequency input and output signals to minimize reflections: pin, nin, clkoutp, clkoutn, dataoutp, dataoutn (also refclkp, refclkn, if a high frequency reference clock is used, such as 155 mhz). it is also necessary for the pin/nin input traces to be matched in length, and the clkoutp/n and dataoutp/n output traces to be matched in length to avoid skew between the differential traces. all high speed cml outputs, clkoutp/n and dataoutp/n, also require 100 ? back termination chip resistors connected between the output pin and vcc. these resistors should be placed as close as possible to the output pins. these 100 ? resistors are in parallel with on-chip 100 ? termination resistors to create a 50 ? back termination (see figure 25). the high speed inputs, pin and nin, are internally terminated with 50 ? to an internal reference voltage (see figure 26). a 0.1 f is recommended between vref, pin 3, and gnd to provide an ac ground for the inputs. as with any high speed mixed-signal design, take care to keep all high speed digital traces away from sensitive analog nodes. 04228-0-023 adn2812 0.1 f 0.1 f 100 ? 100 ? vcc 100 ? 100 ? vcc 50 ? v term v term 50 ? 50 ? 50 ? figure 25. typical adn2812 applications circuit 04228-0-024 c in c in 50 ? 0.1 f 50 ? 3k ? nin pin adn2812 2.5v vref 50 ? 50 ? tia vcc figure 26. adn2812 ac-coupled input configuration soldering guidelines for chip scale package the lands on the 32 lfcsp are rectangular. the printed circuit board pad for these should be 0.1 mm longer than the package land length and 0.05 mm wider than the package land width. the land should be centered on the pad. this ensures that the solder joint size is maximized. the bottom of the chip scale package has a central exposed pad. the pad on the printed circuit board should be at least as large as this exposed pad. the user must connect the exposed pad to vee using plugged vias so that solder does not leak through the vias during reflow. this ensures a solid connection from the exposed pad to vee. choosing ac coupling capacitors ac coupling capacitors at the input (pin, nin) and output (dataoutp, dataoutn) of the adn2812 must be chosen such that the device works properly over the full range of data rates used in the application. when choosing the capacitors, the time constant formed with the two 50 ? resistors in the signal path must be considered. when a large number of consecutive identical digits (cids) are applied, the capacitor voltage can droop due to baseline wander (see figure 27), causing pattern- dependent jitter (pdj). the user must determine how much droop is tolerable and choose an ac coupling capacitor based on that amount of droop. the amount of pdj can then be approximated based on the capacitor selection. the actual capacitor value selection may require some trade-offs between droop and pdj. example: assuming that 2% droop can be tolerated, then the maximum differential droop is 4%. normalizing to v pp : droop = ? v = 0.04 v = 0.5 v pp (1 ? e Ct/ ) ; therefore, = 12 t where: is the rc time constant (c is the ac coupling capacitor, r = 100 ? seen by c). t is the total discharge time, which is equal to n . n is the number of cids. t is the bit period. the capacitor value can then be calculated by combining the equations for and t: r n t c / 12 = once the capacitor value is selected, the pdj can be approximated as ( ) ( ) 6 . 0 / 1 5 . 0 r nt/rc pspp e t pdj ? ? = where: pdj pspp is the amount of pattern-dependent jitter allowed; < 0.01 ui p-p typical. t r is the rise time, which is equal to 0.22/ bw , where bw ~ 0.7 (bit rate). note that this expression for t r is accurate only for the inputs. the output rise time for the adn2812 is ~100 ps regardless of data rate.
adn2812 rev. 0 | page 23 of 28 04228-0-025 50 ? 50 ? pin v ref nin c in c out c out v1 c in v1b v2 v2b tia limamp cdr + ? vcc dataoutp dataoutn 1 v1 v1b v2 v2b v diff 234 vref vth adn2812 v diff = v2?v2b vth = adn2812 quantizer threshold notes: 1. during data patterns with high transition density, differential dc voltage at v1 and v2 is zero. 2. when the output of the tia goes to cid, v1 and v1b are driven to different dc levels. v2 and v2b discharge to the vref level, which effectively introduces a differential dc offset across the ac coupling capacitors. 3. when the burst of data starts again, the differential dc offset across the ac coupling capacitors is applied to the input levels causing a dc shift in the differential input. this shift is large enough such that one of the states, either high or low depending on the levels of v1 and v1b when the tia went to cid, is canceled out. the quantizer does not recognize this as a valid state. 4. the dc offset slowly discharges until the differential input voltage exceeds the sensitivity of the adn2812. the quantizer can recognize both high and low states at this point. figure 27. example of baseline wander dc-coupled application the inputs to the adn2812 can also be dc-coupled. this might be necessary in burst mode applications, where there are long periods of cids, and baseline wander cannot be tolerated. if the inputs to the adn2812 are dc-coupled, care must be taken not to violate the input range and common-mode level require- ments of the adn2812 (see figure 28 through figure 30). if dc coupling is required, and the output levels of the tia do not adhere to the levels shown in figure 29, then level shifting and/or an attenuator must be between the tia outputs and the adn2812 inputs. 04228-0-026 50 ? 0.1 f 50 ? 3k ? nin pin adn2812 2.5v vref 50 ? 50 ? tia vcc figure 28. dc-coupled application 04228-0-027 pin input (v) v pp = pin ? nin = 2 v se = 10mv at sensitivity v se = 5mv min v cm = 2.3v min (dc-coupled) nin figure 29. minimum allowed dc-coupled input levels 04228-0-028 pin input (v) v pp = pin ? nin = 2 v se = 2.0v max v se = 1.0v max v cm = 2.3v (dc-coupled) nin figure 30. maximum allowed dc-coupled input levels
adn2812 rev. 0 | page 24 of 28 coarse data rate readback look-up table code is the 9-bit value read back from coarse_rd[8:0]. table 13. look-up table code f mid 0 5.1934e+06 1 5.1930e+06 2 5.2930e+06 3 5.3989e+06 4 5.5124e+06 5 5.6325e+06 6 5.7612e+06 7 5.8995e+06 8 6.0473e+06 9 6.2097e+06 10 6.3819e+06 11 6.5675e+06 12 6.7688e+06 13 6.9874e+06 14 7.2262e+06 15 7.4863e+06 16 7.4139e+06 17 7.4135e+06 18 7.5606e+06 19 7.7173e+06 20 7.8852e+06 21 8.0633e+06 22 8.2548e+06 23 8.4586e+06 24 8.6784e+06 25 8.9180e+06 26 9.1736e+06 27 9.4481e+06 28 9.7464e+06 29 1.0068e+07 30 1.0417e+07 31 1.0791e+07 32 1.0387e+07 33 1.0386e+07 34 1.0586e+07 35 1.0798e+07 36 1.1025e+07 37 1.1265e+07 38 1.1522e+07 39 1.1799e+07 40 1.2095e+07 41 1.2419e+07 42 1.2764e+07 43 1.3135e+07 44 1.3538e+07 45 1.3975e+07 46 1.4452e+07 47 1.4973e+07 code f mid 48 1.4828e+07 49 1.4827e+07 50 1.5121e+07 51 1.5435e+07 52 1.5770e+07 53 1.6127e+07 54 1.6510e+07 55 1.6917e+07 56 1.7357e+07 57 1.7836e+07 58 1.8347e+07 59 1.8896e+07 60 1.9493e+07 61 2.0136e+07 62 2.0833e+07 63 2.1582e+07 64 2.0774e+07 65 2.0772e+07 66 2.1172e+07 67 2.1596e+07 68 2.2049e+07 69 2.2530e+07 70 2.3045e+07 71 2.3598e+07 72 2.4189e+07 73 2.4839e+07 74 2.5527e+07 75 2.6270e+07 76 2.7075e+07 77 2.7950e+07 78 2.8905e+07 79 2.9945e+07 80 2.9655e+07 81 2.9654e+07 82 3.0242e+07 83 3.0869e+07 84 3.1541e+07 85 3.2253e+07 86 3.3019e+07 87 3.3834e+07 88 3.4714e+07 89 3.5672e+07 90 3.6694e+07 91 3.7792e+07 92 3.8985e+07 93 4.0273e+07 94 4.1666e+07 95 4.3164e+07 code f mid 96 4.1547e+07 97 4.1544e+07 98 4.2344e+07 99 4.3191e+07 100 4.4099e+07 101 4.5060e+07 102 4.6090e+07 103 4.7196e+07 104 4.8378e+07 105 4.9678e+07 106 5.1055e+07 107 5.2540e+07 108 5.4150e+07 109 5.5899e+07 110 5.7810e+07 111 5.9890e+07 112 5.9311e+07 113 5.9308e+07 114 6.0485e+07 115 6.1739e+07 116 6.3081e+07 117 6.4506e+07 118 6.6038e+07 119 6.7669e+07 120 6.9427e+07 121 7.1344e+07 122 7.3388e+07 123 7.5585e+07 124 7.7971e+07 125 8.0546e+07 126 8.3333e+07 127 8.6328e+07 128 8.3095e+07 129 8.3087e+07 130 8.4689e+07 131 8.6383e+07 132 8.8198e+07 133 9.0120e+07 134 9.2179e+07 135 9.4392e+07 136 9.6757e+07 137 9.9356e+07 138 1.0211e+08 139 1.0508e+08 140 1.0830e+08 141 1.1180e+08 142 1.1562e+08 143 1.1978e+08 code f mid 144 1.1862e+08 145 1.1862e+08 146 1.2097e+08 147 1.2348e+08 148 1.2616e+08 149 1.2901e+08 150 1.3208e+08 151 1.3534e+08 152 1.3885e+08 153 1.4269e+08 154 1.4678e+08 155 1.5117e+08 156 1.5594e+08 157 1.6109e+08 158 1.6667e+08 159 1.7266e+08 160 1.6619e+08 161 1.6617e+08 162 1.6938e+08 163 1.7277e+08 164 1.7640e+08 165 1.8024e+08 166 1.8436e+08 167 1.8878e+08 168 1.9351e+08 169 1.9871e+08 170 2.0422e+08 171 2.1016e+08 172 2.1660e+08 173 2.2360e+08 174 2.3124e+08 175 2.3956e+08 176 2.3724e+08 177 2.3723e+08 178 2.4194e+08 179 2.4695e+08 180 2.5233e+08 181 2.5802e+08 182 2.6415e+08 183 2.7067e+08 184 2.7771e+08 185 2.8538e+08 186 2.9355e+08 187 3.0234e+08 188 3.1188e+08 189 3.2218e+08 190 3.3333e+08 191 3.4531e+08
adn2812 rev. 0 | page 25 of 28 code f mid 192 3.3238e+08 193 3.3235e+08 194 3.3876e+08 195 3.4553e+08 196 3.5279e+08 197 3.6048e+08 198 3.6872e+08 199 3.7757e+08 200 3.8703e+08 201 3.9742e+08 202 4.0844e+08 203 4.2032e+08 204 4.3320e+08 205 4.4719e+08 206 4.6248e+08 207 4.7912e+08 208 4.7449e+08 209 4.7447e+08 210 4.8388e+08 211 4.9391e+08 212 5.0465e+08 213 5.1605e+08 214 5.2831e+08 215 5.4135e+08 code f mid 216 5.5542e+08 217 5.7075e+08 218 5.8711e+08 219 6.0468e+08 220 6.2377e+08 221 6.4437e+08 222 6.6666e+08 223 6.9062e+08 224 6.6476e+08 225 6.6470e+08 226 6.7751e+08 227 6.9106e+08 228 7.0558e+08 229 7.2096e+08 230 7.3743e+08 231 7.5514e+08 232 7.7405e+08 233 7.9485e+08 234 8.1688e+08 235 8.4064e+08 236 8.6640e+08 237 8.9438e+08 238 9.2496e+08 239 9.5825e+08 code f mid 240 9.4898e+08 241 9.4893e+08 242 9.6776e+08 243 9.8782e+08 244 1.0093e+09 245 1.0321e+09 246 1.0566e+09 247 1.0827e+09 248 1.1108e+09 249 1.1415e+09 250 1.1742e+09 251 1.2094e+09 252 1.2475e+09 253 1.2887e+09 254 1.3333e+09 255 1.3812e+09 256 1.3295e+09 257 1.3294e+09 258 1.3550e+09 259 1.3821e+09 260 1.4112e+09 261 1.4419e+09 262 1.4749e+09 263 1.5103e+09 code f mid 264 1.5481e+09 265 1.5897e+09 266 1.6338e+09 267 1.6813e+09 268 1.7328e+09 269 1.7888e+09 270 1.8499e+09 271 1.9165e+09 272 1.8980e+09 273 1.8979e+09 274 1.9355e+09 275 1.9756e+09 276 2.0186e+09 277 2.0642e+09 278 2.1132e+09 279 2.1654e+09 280 2.2217e+09 281 2.2830e+09 282 2.3484e+09 283 2.4187e+09 284 2.4951e+09 285 2.5775e+09 286 2.6666e+09 287 2.7625e+09
adn2812 rev. 0 | page 26 of 28 outline dimensions compliant to jedec standards mo-220-vhhd-2 0.30 0.23 0.18 0.20 ref 0.80 max 0.65 typ 0.05 max 0.02 nom 12 max 1.00 0.85 0.80 seating plane coplanarity 0.08 1 32 8 9 25 24 16 17 bottom view 0.50 0.40 0.30 3.50 ref 0.50 bsc 3.25 3.10 sq 2.95 0.60 max 0.60 max 0.25 min top view pin 1 indicator pin 1 indicator 5.00 bsc sq 4.75 bsc sq figure 31. 32-lead frame chip scale package [lfcsp] (cp-32) dimensions shown in millimeters ordering guide model temperature range package description package option adn2812acp ?40c to 85c 32-lfcsp cp-32 adn2812acp-rl ?40c to 85c 32-lfcsp, tape-reel, 2500 pcs cp-32 ADN2812ACP-RL7 ?40c to 85c 32-lfcsp, tape-reel, 1500 pcs cp-32
adn2812 rev. 0 | page 27 of 28 notes
adn2812 rev. 0 | page 28 of 28 notes purchase of licensed i 2 c components of analog devices or one of its sublicensed associated companies conveys a license for the purchaser under the phi lips i 2 c patent rights to use these components in an i 2 c system, provided that the system conforms to the i 2 c standard specification as defined by philips. ? 2004 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d04228C0C3/04(0)

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